The present invention relates to a rotary compressor of variable displacement type, and in particular, to a rotary compressor of variable displacement type suitably used in an air-conditioning system for a vehicle.
In a conventional rotary compressor of variable displacement type as disclosed in Japanese Utility Model Unexamined Publication No. 57-58791, an eccentric rotor rotates in a housing having a suction port and vanes arranged in the rotor compress the fluid suctioned through the suction port and exhaust the compressed fluid through an exhaust port, an inner sleeve being rotatably arranged on the inner surface of the housing. The vanes contact the inner surface of the inner sleeve in a sliding manner, and the inner sleeve is formed with an adjusting port which cooperates with the suction port. The exhaust displacement or volume is controlled by rotating the inner sleeve, i.e. by changing the amount of overlap of the adjusting port with the suction port, in other words, by changing the substantial opening range of the suction opening.
In the above-mentioned prior art, a communication between the suction port and the working space starts when the front vane crosses over the starting point of the opening area formed by the suction port and the adjusting port, and finishes when the rear vane crosses over the terminal point of the opening area. In other words, a suction stroke starts when the front vane crosses over the starting point of the suction port opening range and finishes when the rear vane crosses over the terminal point of the suction port opening range. Consequence, denoting the angular range of the opening area of the suction port with respect to the rotor rotation center by .theta.p, and the angle between adjacent vanes, i.e. the pitch angle of vanes in a circumferential direction by .theta.v, the angular extent or range of the suction stroke is expressed by the sum of .theta.p .theta.v.
In the conventional volume control technique, the suction port opening range .theta.p may be changed, possibly to zero, by rotating the inner sleeve. However, the vane pitch angle .theta.v can not be changed, because the vane pitch angle is determined by the number of vanes. Accordingly, the suction stroke is achieved at least in an angular range .theta.v. Thus, the minimum volume of the working space can not be made smaller than the volume determined by the angle .theta.v, thereby causing a problem that the minimum volume is limited in a volume control operation.